I have over the last few months installed Requiem for the Capital Waistland three times (two of which were clean installs off a fresh download of Fallout New Vegas). All three times I have had a large problem. First, there are no noticeable minor problems, no red triangles that I have seen, no problems with quests or dialogue or anything like that. I have found that as I play through requiem the more I play in the capital waistland my game will develop "problem zones" where if I enter a specific area for whatever reason, and by whatever means, the game will immediently crash, with no warning. This has happened all three different installs, at different times in different areas. My first time it was several areas within DC, for example the "problem zone" that made me finally give up on requiem was right outside the National Library or whatever the building where you need to get the books for Moira for her waistland survival guide quest. Whenever I left the building the game would crash. If I loaded up an earlier save the game would crash when I got there, if I loaded up a much earlier save I could go there, but another "problem zone" would develop later somewhere else. In later installs this exact same thing would happen again. I gave this mod another shot (because I really, really, think it would be a great addition to Fallout New Vegas) but I came across a "problem zone" within a minute of getting through the manhole cover into the capital waistland, when I started walking to vault 101 after about 100 meters the game just crashes. No mater what I do it crashes, i tried tcl to go over it, I tried going a different way, but still within the same area, every time it crashes. If this is going to continue to happen it just would not be worth the time to try to get around these problems over and over again. Does anyone know what is going on with my game? Is there some mod I might be using that is causing this?

Do you also have Fallout 3 installed? It says on the mod's description that it requires both games.

Yes, I have both Fallout New Vegas and Fallout 3 installed on my computer. Then I installed Requiem for the capital waistland, transferring the required files and running the installation program and everything. The game works, requiem works, I can console myself to Megaton and talk to Lucas Sims and do the quests, its just that the more I play the more of these "problem zones" pop up and I cannot ever go to that location again, or it will crash my game. I had fewer problems when I had fewer mods installed. I have FOOK and Project Nevada and a few other UI mods and stuff installed and I wonder if there is any incompatibility that might cause this problem.

From what I read on the page of the Nexus mod:

A. You'll need to follow the install steps 100% to the letter.
B. It works with simple mods, mods an item or two, and so on. However, the more complex a mod, the less likely it'll work properly.
C. It's custom coded, so it's bound to have trouble working properly sometimes.

I am fairly certain that I installed this mod correctly. The instructions say common problems with instillation are missing sounds (like the radio and dialogue) and red triangles all over the place. I have no such problems. The game runs fine, except for the fact that after a while of playing areas will develop where I cannot go there or the game will crash. The only thing I can think of is if mods are conflicting. I am running two FO3 mods (MMM and Fellout for FO3). However, both these mods are said to be compatible with Requiem. I am running some other FNV mods (FOOK, Project Nevada, several UI mods and then mainly minor mods). I am not sure how to test to see if these mods are incompatible. They do not cause immediate crashes on load up or anything. The game will load and play well, but then I will get to an area where my game will crash every time I go there. It might be a building I cannot enter (or leave) without crashing, or just some area in the wilderness that if I get too close to my game crashes. I do not know if this problem is due to bad installation, or mod conflicts or just bad luck. I do not know any way around this problem except to give up on Requiem (something I really do not want to do).

When I first installed RFCW I had the sound issues as there are steps missing in the install instructions. Even though it's a busy thread over on Nexus several times the correct steps have been posted.
I still have one remaining issue but it's not making my game crash, just annoying, and seemingly related to the Broken Steel DLC.

What other mods are you using? Are you using any FO3 mods in your load order as well? (Already answered, oops.) Not usually a problem unless the mod requires FOSE. Most other mods can just be copied over and used just fine. I have mine all as fomods so it's easier to install/uninstall.
The other night I had crashing issues after copying over some mods and narrowed my problem down to Refuge, a house mod. (Now I have to find a new house). Mine was pretty easy as I'd only copied over three Fallout 3 mods.

I tend to think it's a mod problem rather than RFCW itself. And an FO3 mod problem, rather than a New Vegas one. It sounds like you had no problems following the (incomplete) instructions installing and getting it to actually run.
Is it random where it crashes? When it does crash think which mod in your load order could be altering that area (the atmosphere, the NPC's, creatures, buildings, etc) no matter how minor, then disable it and load up the game again. Repeat until the offending mod is found. Have you just tried disabling both MMM and Fellout to see if it is one or both of those?
Or start a fresh new game with only the Fallout NV essentials (DLC's, UI mod, for example) and RFCW then if there are no problems keep adding mods one at a time.

I have thought about doing what you mentioned (disabling all non-essential mods and seeing if it works) however, the problem is that these crashes seem to develop randomly (at least to me). The first time I installed this mod and had this crashing problem was around October-November last year and the only FO3 mod I had was MMM. I was able to travel and play through the capital wasteland for about 15 hours before these areas began to develop, and then they started to occur all over the place. I could usually just avoid them by fast traveling and not going back there (one example is the Anchorage memorial (I think) imminently after finishing the wasteland survival aspect that required going into the Mirelurks nest and placing the thing there). However, once the problem was outside a building that I was already in and there was no way to get out without crashing. I even loaded up a save file from right before I went into the building (thinking that since I had gone into the building before without problems in that save (and only a later save seemed to have the problem) I might be able to get around the problem, but the corruption seemed to follow, and even on the earlier save I could not get out of the building.

I will try to tinker around with my mods, but I cannot see which one could be causing this problem, and even if it is one of them, how do I know if disabling it did anything? These crashes just seemingly randomly pop up all over the place hours into my game.